PROJECT SUMMARY Sexual minorities (lesbian, gay, bisexual and other non-heterosexual individuals) are at increased risk for numerous adverse physical and mental health outcomes, including anxiety, depression, suicidality, substance use, HIV/AIDS, asthma, cardiovascular disease, and certain forms of cancer. Despite clear documentation and replication of these health disparities, relatively little is known about their development from adolescence into adulthood. Two theories primarily dominate the literature. Minority stress models describe unique life stressors experienced only by sexual minorities (e.g., victimization and discrimination based on sexual orientation) as primary contributors to health disparities. Other models implicate both minority stress and normative psychosocial processes together as contributors to health disparities. Some such normative processes include (1) psychological adjustment and characteristics (e.g., emotion regulation/dysregulation, substance use expectancies), (2) disrupted social systems (e.g., family, peers, school), and (3) individual differences (e.g., race/ethnicity, socioeconomic status, temperament). To date, most studies of both minority stress and normative processes are limited by use of cross-sectional samples of primarily Caucasian adults. Although much has been learned from these studies, they do not permit analysis of emerging health disparities across development. Existing research is therefore limited in terms of both generalizability to diverse populations, and validity of directionality inferences between observed ?predictors? and ?outcomes?. My long-term career goals are to identify mechanisms leading to disparities among sexual minorities, with the goal of improving treatments for these disparities, and to develop screening tools to identify high-risk youth who would benefit from prevention programs. To reach this goal, in this project, I address existing limitations to the literature using a prospective sample of individuals who were 14-19 years old at baseline and followed for over 4 years. My goal is to describe developmental trajectories and mechanisms of health disparity development for sexual minority youth compared with heterosexual youth across a 10-year developmental window spanning ages 14- 23 years. Longitudinal outcomes include depression/anxiety, suicidality, delinquency, sleep, general physical health, disordered eating and substance use. Developmental trajectories for these outcomes will be charted by gender and sexual orientation. Confirmatory analyses based on existing literature will be conducted to examine relations between minority stress and adverse outcomes. Then, I will use machine learning to identify as-yet unknown predictors of adverse outcomes and health disparities and characterize any changes in prediction across time. Finally, I will use state-of-the art intervening variable analyses (mediation, moderation) to evaluate longitudinal mechanisms through which health disparities emerge. Findings should provide insight into mechanisms of disparity development and maintenance, informing prevention and intervention strategies.